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PhD Defense by Hao Liu

Hao Liu, Department of Chemistry and Bioscience will defend his thesis on: "Structure, Phase Transitions and Dynamics in Four Special Oxide Glass Systems"

Tidspunkt

09.03.2018 kl. 13.00 - 09.03.2018 kl. 16.00

Beskrivelse

TITLE:

"Structure, Phase Transitions and Dynamics in Four Special Oxide Glass Systems"

ABSTRACT:

The mechanism of phase transition and the composition-structure-property relation are critical for understanding the nature of glass transition and designing glasses with improved properties. However, these issues have not been fully understood owing to the non-equilibrium nature and structural complexity of glasses. The goal of this PhD study is to explore the relations between structure, phase transitions, and dynamics of four special oxide glasses and liquids: Na2O-CaO-B2O3-SiO2, B2O3-Al2O3-SiO2-P2O5, GeO2-BaF2-AlF3, and CaO-Al2O3. The four systems have various glass-forming abilities. Furthermore, they contain abundant structural features which lead to remarkable phenomenon such as non-monotonic variation of glass transition temperature (Tg) with composition.

Considering the four systems together, Tg is found to be sensitive to the change of coordination number of glass network former (e.g., boron and germanium) and intermediate (i.e., aluminum). In addition, when multiple network formers exist, phase separation has great potential to occur in liquids and glasses. In contrast, for the glasses containing less than two typical network formers, structural heterogeneity and polyamorphism occur, leading to special phase transitions such as order-disorder transition upon heating and fragile-to-strong (f-s) transition upon cooling, respectively.

Rheology is important in glass manufacture because it is closely associated with melting and crystallization. Upon cooling below melting temperature, fast crystallization results in the difficulty of the measurement of equilibrium viscosity in the supercooled region. With the development of aerodynamic levitation furnace, we explore viscosity and thermo-physical properties in stable and metastable CaO-Al2O3 liquids covering a wide range of composition. For most glass-forming liquids, the temperature dependence of rheological property is non-Arrhenius and characterized by a single liquid fragility index, whereas the supercooled CaO-Al2O3 liquids exhibit the f-s transition upon cooling. Remarkably, various phase transitions occur in the temperature region of 1.15-1.2Tg for B2O3-Al2O3-SiO2-P2O5, GeO2-BaF2-AlF3, and CaO-Al2O3 systems, reconciling the structural heterogeneity, phase transitions, and abnormal dynamics in this special temperature region.

SUPERVISOR:

  • Professor Yuanzheng Yue

ASSESSMENT COMMITTEE:

  • Associate Professor, Casper Steinmann Svendsen (Chairman), Department of Chemistry and Bioscience, AAU, Denmark
  • Professor, Pierre Lucas, Materials Science & Engineering Department, University of Arizona, USA
  • Professor, Alex Hannon, ISIS Facility, Rutherford Appleton Laboratory, UK

AFTER THE DEFENSE A SMALL RECEPTION WILL BE HELD AT FREDRIK BAJERS VEJ 7H. 

Pris

Free

Arrangør

Department of Chemistry and Bioscience, AAU, Section of Chemistry

Adresse

Fredrik Bajers Vej 7H, 9220 Aalborg Ø, room number: 1.102-6

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